The present invention relates generally to surveillance cameras of the type shown and described in U.S. Pat. No. 3,606,527, the disclosure of which is incorporated herein by reference, and more particularly to a novel film advance control mechanism which prevents film vibration or oscillation, as might be caused by the starting and stopping of the movement of the film relative to the lens assembly.
As described in the aforementioned patent, a surveillance camera of the type under consideration is designed to be started by manual or semiautomatic means upon the occurrence of a robbery in a bank, department store, or the like, and to take pictures of the area at the rate of about a frame a second, for from five to ten minutes.
The intermittent film drive of the aforementioned camera includes a full toothed driven gear and a mutilated drive gear, with the latter being mounted on a drive shaft which can flex laterally in the vicinity of the inter-engaging gears if the top or crown of the lead tooth of the drive gear were to contact the top or crown of a tooth of the driven gear when the gears are reengaged so as to move the film the distance equal to one frame. Although such a relationship occurs infrequently and the tooth of the driving gear promptly slips into position between adjacent teeth on the driven gear, such an occurrence causes a slight variation in the spacing between the frame previously exposed and the frame next to be exposed, and there is some possibility of the drive motor stalling.
The aforementioned camera also includes a flexible belt drive between a pulley on the film driven reel and a pulley on the film takeup reel, with the latter pulley being somewhat larger than the pulley on the film driven reel, whereby to assure there is no buckling of the film between the two reels. However, such a construction results in a limited amount of "slippage" of the flexible belt on the pulley of the film takeup reel when the movement of the film is stopped, which, in turn, causes a slight oscillation of the film driven reel and a possible blurring of the image on the frame of the film then being exposed.
In view of the aforementioned potential problems and deficiencies in what is otherwise a very simple, relatively inexpensive and reliable surveillance camera, it is an object of the present invention to provide a novel film advance control mechanism which assures that the width of the frame or section of film being exposed, is uniform in size.
Another object of the invention is to provide such a novel film advance control mechanism which maintains the film driven reel stationary and without any oscillation whatsoever during the time the film is being exposed, whereby there is no blurring of any of the images as would be caused by movement of the film as it is being exposed.
I have discovered that the above objects and advantages are achieved by providing an arcuate cam segment which is carried by the mutilated drive gear, and an annular cam which is carried by the driven gear, with the annular cam containing an arcuate recess in the outer periphery thereof for receiving the arcuate cam segment in close face to face relationship when the shutter is in the open position, whereby the driven gear and the film driven reel are maintained immobile when the shutter is open and the film is being exposed.
I have also discovered that the meshing of the mutilated drive gear with the driven gear can be achieved without having the gear teeth meet in crown to crown disruptive engagement, by providing a space between adjacent teeth on the driven gear, of a size which is obtained by removing one gear tooth.